XII INTERNATIONAL CONFERENCE AND SEMINAR EDM’2011, SECTION VII, JUNE 30 - JULY 4, ERLAGOL

219

Microwave-Induced Giant Oscillations of the Magnetoconductivity and Zero-Conductance State in 2D Electronic Corbino Disks with

Capacitance Contacts

Dmitriy V. Dmitriev, Igor V. Marchishin, Andrey V. Goran, Alexey A. Bykov

A.V.Rzhanov Institute of Semiconductor Physics, SB RAS, Novosibirsk, Russia Abstract - Using Corbino disks with capacitance contacts, the microwave photoconductivity of the 2D electron gas in selectively doped GaAs/AlAs heterostructures has been studied at 1.6 K in magnetic fields up to 0.5 T. The giant oscillations of the magnetoconductivity and zero – conductance state have been revealed in the samples exposed to microwave radiation at high filling factors similar to those earlier discovered in the 2D Corbino disks with ohmic contacts. The results demonstrate that the presence of ohmic contacts is of no importance for observation of the microwave - induced giant oscillations of the magnetoconductivity and zero – conductance state in the 2D electron system.

Index Terms – 2DEG, microwave, magnetotransport, photoconductivity.

I. INTRODUCTION

IANT MAGNETORESISTANCE oscillations in the two dimensional electron gas (2DEG) system

at high filling factor subject to microwave radiation were first observed about 10 years ago [1], [2]. Till now these oscillations are a subject of many investigations [3], [4]. There is still a discussion about the nature of zero-resistance and zero-conductance states in the minima of these oscillations [5]–[14]. One of the points of interest is the role of ohmic contacts to a 2D electron system on zero-resistance and zero-conductance states. [15], [23], [24]. Both 2DEG and its ohmic contacts are subject to microwave radiation and this may lead not only to the rise of photo-EMF [9], [16]–[19] but also contribute to photoconductivity.

II. RESEARCH RESULTS

In this work, we use the capacitance contacts to the Corbino disk to investigate the 2D electron gas conductivity in selectively doped GaAs/AlAs heterostructures. The structures were grown using molecular beam epitaxy on (100) GaAs substrates. The concentration and mobility of heterostructures were calculated using the van der Pauw method on 5x5 mm square samples with ohmic contacts [20]. The sides of a square were oriented along [110] and [1�10] directions that corresponds to the minimum and

maximum electron mobility in GaAs/AlAs heterostructures [21], [22]. At the temperature T=4.2 K the mobility was �x=170 m2 /Vs and �y=210 m2 /Vs. The concentration of electrons was ne =8x1015 m�2.

Figure 1 (a) shows the scheme of Corbino ring measurements. Originally all the samples were 5x5 mm squares, same as the one used for van der Pauw measurements. Two electrodes were placed at the planar surface of samples. The diameter of the inner electrode was (0.5) mm and the distance between the inner and outer electrodes was 1.5 mm. In the case of ohmic contacts the electrodes were burned. The dc-current resistance between capacitive contacts and the 2D electron gas exceeded 40 M�. The measurements were performed at T = 1.6 K in magnetic field B up to 0.5 T and the measuring current frequency f = 1 MHz. The voltage V0 between contacts in Corbino rings did not exceed 0.1 mV. Lock-in technique was used for measurements of imaginary and real parts of I0. We used a round waveguide with the inner diameter 6 mm to guide microwave radiation of frequency F = 145 GHz to the samples. The samples were placed few millimeters from an open end of the waveguide. The maximum output power of radiation was Pout 4 mW.

Fig. 1. (a) The conductivity measurement scheme in the Corbino geometry.

Metallic electrodes 1 and 2 are in gray. (b) The equivalent scheme of a Corbino ring with Ohmic contacts. (c) The equivalent scheme of a Corbino

ring with capacitive contacts

G

ISBN 978-1-61284-795-5/11/$26.00 ©2011 IEEE

XII INTERNATIONAL CONFERENCE AND SEMINAR EDM’2011, SECTION VII, JUNE 30 - JULY 4, ERLAGOL

220

Figure 1(b) shows the equivalent scheme of Corbino ring with ohmic contacts. G denotes the conductivity of a 2DEG between ohmic contacts. Figure 2 shows the experimental curves of conductivity with and without microwave radiation. The oscillating component appears in the presence of microwave radiation, its maxima are marked by numbers 1, 2, 3, and 4. The position of the maxima is determined by j��/�c where j=1,2,3. . . are positive integers. It is clearly seen that the conductivity between the maxima 1 and 2 is very close to zero, which is in agreement with results presented in Refs. [8] and [11].

Fig. 2. G(B) measured on a 2D Corbino ring with Ohmic contacts

with and without microwave radiation of frequency 145 GHz. Blue line corresponds to Pout=0, red line corresponds to Pout=4 mW. The

arrow marks the cyclotron resonance.

Figure 1 (c) shows the equivalent scheme of Corbino ring with capacitive contacts. The voltage V0 is applied to capacitive contacts 1 and 2 with capacitances C1 and C2, respectively. We can replace these capacitances with an equivalent capacitance C=C1C2 / (C1+C2) and taking into account that C1��C2, we can write C�C1. The electric current I0 of the frequency f, going through a Corbino ring with capacitive contacts, can be written as follows:

� �fCiGVI �2/1/1/00 � (1) Using relation (1), we can readily demonstrate that C is specified by the equality:

� � � � �0002

02 Im/ImRe2 IVIIfC �� (2)

Fig. 3. Magnetic field dependences of C measured at the 2D electronic Corbino disk with capacitance contacts in the (thin lines) absence and (thick lines) presence of 145 GHz microwave radiation

The C(B) dependences calculated by formula (2) are presented in Figure 3. These curves demonstrate that Cweakly depends on the magnetic field B < 0.6 T (varies by less than 10%) and is almost independent of the microwave radiation. This behavior of C(B) makes it possible to use the equivalent circuit of the Corbino disk, where the capacitance C is constant, and to apply formula (3) to calculate the conductivity G.

� � � � �G (3) 000

20

2 Re/ImRe IVII �Figure 4 shows the curves of G(B) calculated using (3).

With no microwave radiation the value of G decreases monotonically with the increase in magnetic field, while in the presence of radiation an oscillating component appears in G(B). This component is fully identical to giant oscillations of magnetoconductivity presented in Fig. 2.

Fig. 4. G(B) calculated for a 2D Corbino ring with capacitive electrodes with and without microwave radiation of frequency 145 GHz Blue line corresponds to Pout=0, red line corresponds to Pout=4 mW. The arrow

marks the cyclotron resonance.

III. CONCLUSION

To summarize, in this paper we have shown that microwave induced conductivity measured in a 2D electron gas at large filling factor in Corbino ring geometry is identical when using Ohmic and capacitive contacts. It has been experimentally shown that Ohmic contacts are not important for observation of microwave-induced zero-conductance states in 2D electron systems at large filling factor.

The work was supported by RFFI Project No. 11-02-00925.

REFERENCES [1] M. A. Zudov, R. R. Du, J. A. Simmons, and J. L. Reno, Phys. Rev. B

64, 201311(R) 2001. [2] P. D. Ye, L. W. Engel, D. C. Tsui, J. A. Simmons, J. R. Wendt, G. A.

Vawter, and J. L. Reno, Appl. Phys. Lett. 79, 2193 2001. [3] O. M. Fedorych, M. Potemski, S. A. Studenikin, J. A. Gupta, Z. R.

Wasilewski, and I. A. Dmitriev, Phys. Rev. B 81, 201302(R) 2010. [4] M. Khodas, H.-S. Chiang, A. T. Hatke, M. A. Zudov, M. G. Vavilov,

L. N. Pfeiffer, and K. W. West, Phys. Rev. Lett. 104, 206801, 2010. [5] R. G. Mani, J. H. Smet, K. von Klitzing, V. Narayanamurti, W. B.

Johnson, and V. Umansky, Nature (London) 420, 646, 2002. [6] M. A. Zudov, R. R. Du, L. N. Pfeiffer, and K. W. West, Phys. Rev.

Lett. 90, 046807, 2003. [7] S. I. Dorozhkin, JETP Lett. 77, 577 2003. [8] C. L. Yang, M. A. Zudov, T. A. Knuuttila, R. R. Du, L. N. Pfeiffer, and

K. W. West, Phys. Rev. Lett. 91, 096803, 2003.

DMITRIEV et al.: MICROWAVE-INDUCED GIANT OSCILLATIONS… 221

[9] R. L. Willett, L. N. Pfeiffer, and K. W. West, Phys. Rev. Lett. 93, 026804, 2004.

[10]A. A. Bykov, A. K. Bakarov, D. R. Islamov, and A. I. Toropov, JETP Lett. 84, 391, 2006.

[11]A. A. Bykov, JETP Lett. 87, 551, 2008. [12]A. V. Andreev, I. L. Aleiner, and A. J. Millis, Phys. Rev. Lett.

91, 056803, 2003. [13]I. G. Finkler and B. I. Halperin, Phys. Rev. B 79, 085315, 2009. [14]A. D. Chepelianskii and D. L. Shepelyansky, Phys. Rev. B 80,

241308(R) 2009. [15]I. V. Andreev, V. M. Muraviev, I. V. Kukushkin, J. H. Smet, K.

von Klitzing, and V. Umanskii, JETP Lett. 88, 616, 2008. [16]A. A. Bykov, JETP Lett. 87, 233, 2008. [17]S. I. Dorozhkin, I. V. Pechenezhskiy, L. N. Pfeiffer, K. W. West,

V. Umansky, K. von Klitzing, and J. H. Smet, Phys. Rev. Lett. 102, 036602, 2009.

[18]I. A. Dmitriev, S. I. Dorozhkin, and A. D. Mirlin, Phys. Rev. B 80, 125418, 2009.

[19]A. A. Bykov, JETP Lett. 91, 361, 2010. [20]O. Bierwagen, R. Pomraenke, S. Eilers, and W. T. Masselink,

Phys. Rev. B 70, 165307, 2004. [21]A. A. Bykov, A. K. Bakarov, A. V. Goran, A. V. Latyshev, and

A. I. Toropov, JETP Lett. 74, 164, 2001. [22]A. A. Bykov, D. R. Islamov, A. V. Goran, and A. K. Bakarov,

JETP Lett. 86, 779, 2007. [23]A. A. Bykov, I. V. Marchishin , JETP Lett. 92, No.1, 2010 [24]A. A. Bykov, I. V. Marchishin, A. V. Goran, D. V. Dmitriev,

APL97, 082107, 2010

Dmitriy V. Dmitriev is a scientific research worker in the Institute of Semiconductor Physics. He received the Master’s degree from the Novosibirsk State Technical University in 2002.